Interrupted jet air knife for sheet separator

ABSTRACT

An automatic document handler adapted to receive a stack of documents to be copied for feeding the documents seriatim to the platen of a copy machine and returning the copied documents to the stack. A combination vacuum-belt document separator in conjunction with a multiple orifice air knife and a document tray having a &#34;U&#34; shaped pocket is provided to assure positive feeding of documents without misfeeds or multifeeds.

BACKGROUND OF THE INVENTION

With the advent of high speed xerographic copy reproduction machineswherein copies can be produced at a rate in excess of three thousandcopies per hour, the need for a document handler to feed documents tothe copy platen of the machine in a rapid, dependable matter wasrecognized to enable full utilization of the reproduction machinespotential copy output. A number of document handlers are currentlyavailable to fill that need. These document handlers must operateflawlessly to virtually eliminate the risk of damaging the originals andgenerate minimum machine shutdowns due to uncorrectable misfeeds ordocument multifeeds. It is in the initial separation of the individualdocuments from the document stack where the greatest number of problemsoccur.

Since the documents must be handled gently but positively to assureseparation without damage through a number of cycles, a number ofseparators have been suggested such as friction rolls or belts used forfairly positive document feeding in conjunction with a retard belt, pad,or roll to prevent multifeeds. Vacuum separators such as sniffer tubes,rocker type vacuum rolls, or vacuum feed belts have also been utilized.

While the friction roll-retard systems are very positive, the action ofthe retard member, if it acts upon the printed face can cause smearingor partial erasure of the printed material on the document. With singlesided documents, this does not present a problem as the separator can bedesigned so that the retard mechanism acts upon the underside of thedocument. However, with documents printed on both sides, there is no wayto avoid the problem. Additionally, the reliable operation of frictionretard feeders is highly dependent on the relative frictional propertiesof the paper being handled. This cannot be controlled in a documentfeeder.

It is therefore the object of this invention to provide an improvedvacuum feeder which consistantly feeds sheets in a positive yet gentlemanner without multifeeds.

SUMMARY OF THE INVENTION

A sheet feeder having an improved air knife for separating and feedingthe bottom sheet in a sheet stack, the feeder including a stack trayhaving a pocket formed therein and a vacuum feed belt assemblypositioned in the pocket below the surface of the tray, the air knifebeing provided with a plurality of sharp edged orifices arranged toprovide a plurality of air streams directed at approximately a 30° angledownwardly toward the lead edge of the bottom sheet, the air stream fromeach orifice diverging into dead air space between the jets, expansionof each stream inducing velocity and pressure gradients along its coursefor optimum feeder performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary document handleremploying the sheet separatorfeeder of the present invention.

FIG. 2 is an enlarged, cross-sectional view of the separator-feederportion of the document handler of FIG. 1.

FIG. 3 is an end view, partially in section of the vacuum feed beltsillustrated in FIG. 2.

FIG. 4 is a top view of the document tray and feed belts of the documenthandler illustrated in FIG. 1.

FIG. 5 is a partial perspective view of the discharge end of the airknife illustrating the air discharge orifices.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is illustrated an automatic documenthandler 1 for installation above the exposure platen 3 of a xerographicreproduction machine. The document handler is provided with a documenttray 5 to be explained more fully hereinafter, adapted for supporting astack of documents 7 face up. A vacuum beltcorrugating feeder mechanism9 is located below the document tray for acquiring and corrugating thebottom document in the stack and forwarding the document to take awayroll pair 11 after an air knife 12 has had time to separate sheet 1 fromthe rest of the stack. The document is then fed by take-away roll pair11 through document quide 13 to feed-roll pair 15 and under platen belt17 onto the platen of the copy machine for reproduction. After exposureof the document, it is fed off the platen by belt 17 into guide 19 andfeed-roll pairs 21 and 23 either to an inverter mechanism 25 or back tothe document stack through the feed-roll pair 27. A diverter 29 isprovided to divert the document either to the inverter or to thefeedroll pair 27. The inverter comprises a three roll arrangement 31 anda closed inverter pocket 33. If the document is to be inverted it is fedthrough the lower two rolls of the three roll inverter into the pocket.When the trail edge of the document clears the nip of the lower tworolls in the three roll inverter, the stiffness of the sheet will causethe trail edge to straighten up into the nip of the upper two rolls ofthe inverter at which time it will be fed into roll pair 27 and backinto the document stack. The inverter pocket illustrated is sized suchthat when the leading edge of the document contacts the end of thepocket, the document will buckle slightly within the upper portion ofthe pocket 33, the buckle thereby providing the required force to feedthe trailing edge of the document into the upper roll pair of theinverter rolls for feeding the sheet toward roll pair 27. If desired, anopen ended inverter pocket could be utilized having a feed roll pairassociated therewith for feeding the document back into the upper rollpair in a positive manner rather than relying on the sheet buckle tofeed the document thereto. The document handler is also provided with asheet separator finger 35 as is well known in the art to separate thedocuments to be fed from those documents returned to the documenthandler. Upon removal of the last document from beneath sheet separatorfinger 35, the finger 35 drops through a slot provided in the tray,suitable sensors are provided to sense that the last document in the sethas been removed from the tray and the finger is then rotated in aclockwise direction to again come to rest on the top of the documents inthe stack prior to subsequent recirculation of the document set.

Referring more particularly to FIGS. 2, 3 and 4 wherein the noveldocument separator-feeder is more clearly illustrated, there isdisclosed a plurality of feed belts 37 supported for movement on feedbelt rolls 38, 39, and 40. Spaced within the run of the belts 37 thereis provided a vacuum plenum 41 having openings 43 therein adapted forcooperation with perforations 45 in the belts 37 to provide a vacuum forpulling the bottom documents in the document stack onto the belts 37. Ascan be seen from FIG. 3, the plenum is provided with a raised portion 48beneath the center belt run so that upon capture of the bottom documentin the stack against belts 37, a center corrugation will be produced inthe bottom sheet. Note also that the belts are below the surroundingsupport surfaces. Thus the document is corrugated into a double valleyconfiguration. The flat surfaces of the vacuum belts on each side of theraised center belt generates a region of maximum stress in the documentwhich varies with the document beam strength. In the unlikely event thatmore than one document is pulled down into contact with the feed belts,the beam strength of the second document resists the corrugating action,thus gaps are opened between sheets one and two which extend to theirlead edges. These gaps and channels reduce the vacuum levels betweensheets one and two due to porosity in sheet one and provide for entry ofthe separating air flow from the air knife 12. The air knife 12comprised of pressurized air plenum 50 having a plurality of air jetopenings 51 is provided to inject air between the document pulled downagainst the feed belt and the documents thereabove to provide an aircushion or bearing between the stack and the bottom document to minimizethe force necessary for removing the bottom document from the stack. Itcan be seen by reference to FIG. 4 that the air knife 12, rather thanhaving a long, continuous slot to discharge air into the lead edge ofthe stack to separate the bottom sheet from the remainder of the stackby establishing an air cushion therebetween, is provided with aplurality of separated discharge orifices 51. By providing separatedorifices, a dramatic improvement in the effectiveness of the dischargedair to provide the desired air cushion or sheet separation is achieved.It appears that the air stream or jet emerging from each orificediverges and expands into the dead air space between the jets. Thisdiversion and expansion of the streams induces both velocity andpressure gradients in the discharged air which results in a moreeffective air cushion at lower air discharge rates. It can be understoodthat if two documents are pulled down toward the belts 37, since the topsheet would not be corrugated, the air knife would inject air into thespace between the two documents and force the second document off fromthe raised belt back toward the document stack. Control of the height towhich the stack is raised by the air pressure under sheet two isprovided by openings such as cutaway 52 in the side wall (FIG. 1) andopenings in the rear wall (not shown). These openings vent the air undersheet two when the stack is lifted to the height of the openings.

If the document feeder is to be used with large document stacks wherethe air knife might be insufficient to provide the desired air bearingbetween the bottom document and the remainder of the stack,supplementary side air jets may be utilized although they have beenfound to be unnecessary for the conditions normally encountered incurrent reproduction machines.

While perforated belts cooperating with openings in the vacuum plenumhave been disclosed, it may be desireable to use "O" ring type feedbelts with the vacuum plenum perforations located between the belt runsrather than beneath the belts. If "O" ring type feed belts are usedhowever, the number of belts must be increased so that the spacingbetween belts is small enought to prevent the document being drawn downinto contact with the vacuum plenum. Additionally the plenum surfaceshould be raised up between the "O" ring belts in the region of thedocument lead edge. This raised portion is to minimize vacuum air flowunder lead edge of the bottom sheet after it has been acquired. Thishelps prevent multifeeds when the lead edge of the second sheet isfurther forward then lead edge of the bottom sheet.

By suitable valving and controls, it is desirable to provide a delaybetween the time the vacuum is applied to pull the document onto thebelts and the start up of the feed belts to assure that the bottomdocument is captured on the belt before belt movement commences and toallow time for the air knife to separate sheet 1 from any sheets thatwere pulled down with it.

By reference to FIGS. 1, 2 and 4 it can be seen that the document tray 5is provided with a depressed portion or pocket 53 having a generallyparabolic outline behind the feed belt assembly. This pocket serves anumber of purposes. First, space is provided for the forward portion ofthe bottom document to be pulled down onto the feed belt assemblyproviding for formation of the two valley corrugation previouslymentioned. Secondly, the vacuum is applied over the area of the pocketwith an air seal between the bottom document provided by the parabolicedges of the pocket. The air seal maximizes the vacuum force over thewhole area of the pocket thus helping to pull the bottom document ontothe feed belt assembly. A third function of the parabolic pocket is toprovide for a high pressure seal between sheet 1 and the remainder ofthe stack. This high pressure seal is achieved by supporting a majorportion of the stack weight in the edge regions of the pocket. The sealserves to reliably convert the velocity energy of the air knife flowinto a lifting pressure over the pocket area. One desirableimplementation is to have the air knife discharge air only in the regionopposite the pocket.

To further increase the efficiency of the system, the stack tray isprovided with a rearward tilt as seen in FIGS. 1 and 2. When floatationair is provided under the stack or between the first and second sheets,gravity will allow the sheets to settle or float back against the reartray wall. Thus, the sheet being removed is pulled uphill while gravityhelps hold the remainder of the sheets back, helping to preventmultifeeds.

With this disclosed arrangement of pocket geometry, improved air knifeand spaced, corrugating feed belt assembly, optimum document separationand feed can be obtained without the necessity for retard members ormultiple sheet stops. Further the system is extremely gentle yetpositive.

While I have described a preferred embodiment of my invention, it shouldbe understood that the invention may be otherwise embodied within thescope of the following claims.

What is claimed is:
 1. A bottom sheet separator-feeder for separatingand forwarding sheets seriatim comprising;a stack tray adapted forsupporting a stack of sheets to be fed, said tray having a depressedpocket formed therein so that the major portion of the stack weight issupported by the edge portions of said pocket to provide a seal betweenthe sheets and the edge portions of said pocket; vacuum feed meansdisposed beneath said tray adapted to pull the bottom sheet in the stackinto said pocket and feed the sheet from beneath the sheet stack; and,an air knife disposed adjacent the front of said tray to inject airbetween the bottom sheet in the stack on said tray and between adjacentsheets in the stack, said air knife having a plurality of spaceddischarge orifices therein, movement of the bottom sheet in the stackinto said pocket by said vacuum feed means causing a pocket shapeddepression in the bottom sheet, thereby providing a space between thebottom sheet and the remainder of the stack for injecting air thereinfrom said air knife, the plurality of discharge orifices in said airknife providing a plurality of diverging and expanding air streams toinduce velocity and pressure gradients in the space between the bottomsheet and the remainder of the stack above said pocket to provideoptimized air flow over the top of the bottom sheet for supporting theremainder of the stack spaced from the bottom sheet.
 2. A bottom sheetseparator according to claim 1 wherein said discharge openings in saidair knife are located opposite said pocket.